i) Field of the Invention
The present invention relates to a high-frequency magnetic material exhibiting a high magnetic permeability at high frequencies, and to a method for producing the material. More particularly, the present invention relates to a high-frequency magnetic material which is useful at high frequencies ranging from 10 MHz to several tens of gigahertz, and to a method for producing the material.
ii) Related Art
A magnetic material is recently applied to an inductor, electromagnetic wave absorber, magnetic ink, and the like, and the importance of the magnetic material is increasing. In connection with a magnetic material used in these applications, a real part (μ′) of a magnetic permeability or an imaginary part (μ″) of the magnetic permeability is utilized. For instance, a high μ′ (or low μ″) is utilized for an inductor, and a high μ″ is utilized for an electromagnetic wave absorber. Therefore, when a magnetic material is actually used as a component, μ′ and μ″ must be controlled in accordance with an operating frequency band of an electronic device. In recent years, since the operating frequency band of the electronic device has become higher, a strong demand exists for a technique for producing a material whose μ′ and μ″ can be controlled at high frequencies.
Ferrite and an amorphous alloy are principally used as a magnetic material for an inductor employed at high frequencies of 1 MHz or more. These magnetic materials do not induce a loss (low μ″) at frequencies of 1 MHz to 10 MHz and exhibit a high μ′ and a superior magnetic characteristic. However, the real part μ′ of magnetic permeability of these magnetic materials decreases at higher frequencies of 10 MHz or more, and sufficient characteristics are not necessarily acquired.
For these reasons, development of an inductor utilizing a thin-film technique, such as sputtering or plating has been performed actively. However, the thin-film technique, such as sputtering, requires a large-size facility and precise control of a film thickness, or the like. Therefore, the thin-film technique is not well sufficient in terms of cost and yield. Further, an inductor manufactured by the thin-film technique lacks long hours of thermal stability of a magnetic characteristic at high temperatures and high humidity.
On the other hand, the electromagnetic wave absorber absorbs noise by means of utilization of high μ″, thereby preventing occurrence of failures in electronic equipment. The electronic equipment includes a semiconductor element, such as an IC chip, or various types of communications equipment. Such electronic equipment includes various devices; for example, a device used at a frequency range of one megahertz to several gigahertz or a device used at high frequencies of several tens of gigahertz or more. Recently, the number of pieces of electronic equipment used at high frequency ranges of 1 GHz or more particularly tends to increase. An electromagnetic wave absorber of electronic equipment used at high frequencies has hitherto been manufactured by means of a binder molding technique for mixing ferrite particles, carbonyl iron particles, FeAlSi flakes, FeCrAl flakes, or the like, with a resin. However, these materials exhibit extremely-low μ′ and μ″ at high frequencies of 1 GHz or more, and a sufficient characteristic has not been acquired.
A material synthesized by means of a mechanical alloying technique, or the like, lacks long hours of thermal stability, and provides low yield.
A high-frequency magnetic material containing irreducible metal oxide and magnetic metal particles deposited on the surface and inside of the oxide has been known (JP-A-2004-281846). Moreover, there has been known a technique for producing a composite oxide sintered body by means of causing irreducible metal oxide, a magnetic metal oxide, and an oxide-based sintering aids to react with one another and reducing the composite oxide sintered body, thereby producing composite oxide with metal particles (Japanese Patent No. 3776839).